These are trainer groups with "unused" trainer ids. The "find_trainer_ids_from_scripts" function analyzes each script in the game, and each map header in the game (because of code in TrainerFragment), and finds all references to trainers. But, if there are any trainers that are referenced in raw ASM, this method does not detect them. Each instance of a trainer reference is added to a global table called "trainer_group_maximums". Next, "find_trainer_ids_from_scripts" looks at the trainer IDs referenced for each group and takes the minimum number and the maximum number. To find whether or not there are any unused trainers, it takes the minimum and maximum ids and then sees which intermediate numbers are missing from the list of "referenced" trainer ids.

update: this output is moved into "report_unreferenced_trainer_ids".

trainer group 0x19 ("Lass") (min=0x1, max=0x11) has 2 unreferenced trainer ids: [12, 13]
trainer group 0x1b ("CooltrainerM") (min=0x1, max=0x14) has 4 unreferenced trainer ids: [18, 13, 14, 15]
trainer group 0x1d ("Beauty") (min=0x1, max=0x11) has 11 unreferenced trainer ids: [3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 15]
trainer group 0x1f ("Rocket_Grunt") (min=0x1, max=0x1f) has 6 unreferenced trainer ids: [12, 22, 23, 26, 27, 30]
trainer group 0x20 ("Gentleman") (min=0x1, max=0x5) has 1 unreferenced trainer ids: [4]
trainer group 0x26 ("SwimmerM") (min=0x1, max=0x15) has 8 unreferenced trainer ids: [9, 10, 11, 12, 13, 16, 19, 20]
trainer group 0x27 ("SwimmerF") (min=0x1, max=0x13) has 6 unreferenced trainer ids: [8, 9, 10, 11, 13, 16]
trainer group 0x29 ("Super_Nerd") (min=0x2, max=0xe) has 5 unreferenced trainer ids: [11, 12, 3, 4, 5]
trainer group 0x30 ("Firebreather") (min=0x1, max=0x8) has 2 unreferenced trainer ids: [2, 3]
trainer group 0x32 ("Blackbelt") (min=0x2, max=0x9) has 1 unreferenced trainer ids: [3]
trainer group 0x36 ("Camper") (min=0x1, max=0x16) has 6 unreferenced trainer ids: [9, 10, 14, 15, 16, 17]
trainer group 0x39 ("Medium") (min=0x1, max=0x7) has 3 unreferenced trainer ids: [3, 4, 5]
trainer group 0x3b ("Pokefan") (min=0x1, max=0xe) has 2 unreferenced trainer ids: [10, 11]
trainer group 0x3e ("Pokefan") (min=0x1, max=0x6) has 2 unreferenced trainer ids: [3, 4]

total unused trainers: 59